Method of removing aluminum oxides from aluminum-killed steels and steels produced by such method



J 8, 1964 e. P. CONTRACTOR ETAL 3, 59

METHOD OF REMOVING ALUMINUM oxznss FROM ALUMINUMKILLED STEELS AND STEELS PRODUCED BY SUCH METHOD Filed Sept. 2'7, 1961 PATENT AGENT United States Patent 'O 3,119,159 METHUD F REMOVING ALUMINUM GEE FROM ALUMHNUM-KILLED STEEL AND STEELS PRQDUCED BY SUCH METHOD Gustad P. Contractor and Robert K. Ruhr, Ottawa, Ontario, Canada, assignors to Her Majesty The Queen In Right of Canada as represented by the Minister of Mines and Technical urveys Filed Sept. 27, 1961, Ser. No. 141,042 2 Claims. (Ci. 22-415) This invention relates to a method of removing aluminum oxides from aluminum-killed steels and steels produced by such method.

Aluminum-killed steels of plain carbon and other types are subject to the well-recognized disadvantages incident to the presence of aluminum oxide (A1 0 in the steel produced. The aluminum oxide tends to occur in the steel in galactic concentrations which manifest themselves in streaks in the final product. If these streaks occur on the surface of the steel they permanently mar the appearance thereof and the steel is thus unacceptable for many purposes and must be rejected. Even if the steel product is to be coated, as in galvanizing, the aluminum oxide streaks are not tolerable because they adversely affect the adhesion of the coating. These aluminum oxide concentrations, whether internally or externally of the final product, further deleteriously afiect the strength and corrosion resistant properties of the steel.

It is an object of this invention to provide a method of producing aluminum-killed steels in which aluminum oxide concentrations are substantially eliminated.

Another object is to provide a method of producing aluminum-killed steels in which aluminum oxide concentrations are substantially eliminated and in which the total oxygen content is sharply reduced.

Another object is to provide an aluminum-killed steel of low alumina and oxygen content.

The invention will be described with reference to the accompanying drawings, in which FIGURES 1, 2 and 3 are sectional elevations oi ingots produced in accordance with the invention.

Broadly, the invention resides in the steps of adding small amounts of uranium to the steel melt to form high density uranium compounds therein, pouring the melt into a mold, permitting the high density uranium compounds to settle by gravity in the melt before solidification thereof occurs, allowing the melt to solidify in the mold to form an ingot having a lower segregated portion of minor extent containing the uranium compounds and an upper unse regated portion of major extent, and separating the unsegregated portion from the segregated portion.

It has been determined that the addition of small amounts of uranium to molten aluminum-killed steel results in conversion of the A1 0 formed in the melt by the addition of aluminum to a high density uranium compound or compounds, probably in the form of uraniumaluminum oxides. Because these compounds are more dense than the molten steel, they sink by gravity to the bottom of the poured ingot or casting provided the cooling rate is sufficiently low to permit substantially complete settling before solidification occurs.

Control of the cooling rate may readily be eifected by, for instance, suitable choice of shape and size of ingot mold. For example, choice of a relatively thin-walled ingot mold which produces an ingot whose height to diameter ratio is low, will result in a sufficiently low cooling rate for the purposes of the invention.

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The uranium is added to the steel melt in the ladle in the range of 0.010% to 0.20%, preferably 0.05% to 0.10% of the melt.

Settling of the uranium compounds produces a segregated ingot portion of minor extent adjacent the bottom thereof containing such compounds and an unsegregated portion of major extent adjacent the top thereof. It is relatively easy to determine the extent of the segregated and unsegregated portions by examination and/or analysis. Thus, the segregated portion may be separated from the ingot leaving a substantially uniform unsegregated portion containing steel of high quality and free from any A1 0 concentrations.

It has also been found that the treatment described results in a marked reduction in total oxygen content of the steel. While such reduction is due in large part to the removal of the A1263, it is believed that the uranium also combines with other free oxygen and other oxides resent to form a uranium oxide or oxides which, being more dense than molten steel, also sink into the bottom segregated portion.

If desired, the uranium in the segregated portions may be recovered in any suitable manner.

A series of tests have been carried out in a conventional induction furnace. The metal was tapped at 1620" 01-10 C. into a ladle, 2 lb./ton A1 being added to the tap stream. The uranitun was wrapped in aluminum foil and wired onto a steel plunging rod. The uranium was plunged and stirred into the ladle of molten metal when the metal temperature was 1585 Ci10 C. The ingot was then poured, together with a small bar for chemical analyses.

A. /2 in. slice was cut from the ingot along the longitudinal centre-line. This slice was milled and surface ground, and then an vautoradiograph obtained of the full section. Sulphur prints and deep etching in 1:1 HCl at C. were then carried out on the slice. Autoradiographs and deep etching were used as a guide to obtain d-rillings from areas free of obvious uranium segregation, as Well as from the segregated areas. Solid samples were also cut from both areas, for oxygen and nitrogen analyses and for metallograph-ic examination.

The chemical analyses obtained from the small bars (referred to as spoon samples) poured with each ingot are listed below in Table I:

TABLE I Spoon Sample Analyses Percent Element Heat No. 1 Heat No. 2 Heat N0 3 Acid Insol U 0. 102 0. 036

1 Uranium was added as pure metal to Heat 1, as 50% Al-U alloy to Heat 2, and as low carbon 50% FeU alloy to Heat 3.

FIGURES 1 to 3 are drawings of the autoradiographs obtained of the respective Heats l, 2 and 3.

ingot 1 in FEGU'RE 1 has a clearly defined segregated portion .2. and an unsegregated portion 3. Table II below 3 gives the analyses for the various locations 1, 2, 3, 4, 5, A and B indicated on the drawing:

TABLE II Location Pcr- Per- Per- Pcr- Per- Per- Per- (clegiz cent cent cent cent cent cent 1 0g and N2 analyses by vacuum iusion technique. Figures shown are an average of two determinations.

Ingot 4 in 'FIGURE 2 also has a clearly defined segregated portion 5 and an unsegregated portion 6. Table III below gives the analyses for the various locations indicated:

TABLE III Location Ingot 7 in FIGURE 3 has a segregated portion 8 and an unsegregate'd portion 9. Table IV below gives the analyses at various locations:

Reference to the drawings, as well as to photomicrographs of samples cut from the unsegregated and segregated areas of the ingots of the sample tests, clearly shows that the addition of uranium to the steels has resulted in the formation of compounds denser than molten steel and that such dense compounds settle to the bottom of the ingot in a clearly defined segregated area. Analyses shows the segregated portions of the ingots, in all cases, to be high in uranium, oxygen, and alumina.

The unsegregated portions of the ingots are shown to be exceptionally low in oxygen and consequently acid insoluble aluminum (A1 0 The total oxygen content is between 0.001% and 0.002%, which is lower than that normally found even in vacuum stream degassed ingots. This low total oxygen content is coupled with extremely low 0.001%) A1 0 content.

We claim:

1. A method of producing steel which comprises adding uranium to an aluminum-k illed steel melt in an amount of 0.010% to 0.20% of said melt to form uraniurn aluminum oxide compounds therein of higher density than molten steel, pouring said melt into a mold, permitting said uranium compounds to settle by gravity in said melt before solidification thereof, said melt on solidification in said mold forming an ingot having a lower segregated portion of minor extent containing said uranium compounds and an upper unsegregated portion of major extent substantially free of said uranium compounds, and separating said lower segregated portion from said ingot.

2. A method of producing steel as defined in claim 1, said uranium being added to said melt in an amount of 0.05% to 0.10% of said melt.

References Cited in the file of this patent UNITED STATES PATENTS 722,270 Weber Mar. 10, 1903 754,262 Weber Mar. 8, 1904 1,210,625 Flannery Jan. 2, 1917 1,247,252 Flannery Nov. 20, 1917 1,415,733 Thofehrn May 9, 1922 2,236,504 Herty Apr. 1, 1941 2,290,273 Burgess July 21, 1942 2,980,529 Knapp et al Apr. 1 8, 1961 

1. A METHOD OF PRODUCING STEEL WHICH COMPRISES ADDING URANIUM TO AN ALUMINUM-KILLED STEEL MELT IN AN AMOUNT OF 0.010% TO 0.20% OF SAID MELT TO FORM URANIUM ALUMINUM OXIDE COMPOUNDS THEREIN OF HIGHER DENSITY THAN MOLTEN STEEL, POURING SAID MELT INTO A MOLD, PERMITTING SAID URANIUM COMPOUNDS TO SETTLE BY GRAVITY IN SAID MELT BEFORE SOLIDIFICATION THEREOF, SAID MELT ON SOLIDIFICATION IN SAID MOLD FORMING AN INGOT HAVING A LOWER SEGREGATED PORTION OF MINOR EXTENT CONTAINING SAID URANIUM COMPOUNDS AND AN UPPER UNSEGREGATED PORTION OF MAJOR EXTENT SUBSTANTIALLY FREE OF SAID URANIUM COMPOUNDS, AND SEPARATING SAID LOWER SEGREGATED PORTION FROM SAID INGOT. 